The present invention relates to an engine igniting coil device.
Recently, there has been developed such an engine igniting coil device which comprises one coil case wherein a plurality of coil units selected in accordance with the quantity of engine cylinders are arranged without using a distributor and integrally molded by potting with insulating material such as epoxy resin and the like.
In the ignition coil device, each coil unit is composed of a primary coil bobbin incorporating a center core with a primary coil in its hollow portion and a secondary coil bobbin coaxially fitted thereon with a connecting core disposed outside the coil bobbin so as to face, at both its end faces with a specified gap to respective end faces of the center core to form a closed magnetic circuit therebetween.
The above-mentioned coil unit has no means for determining the position of the connecting core in relation to the center core mounted in the hollow portion of the primary coil bobbin when the connecting core is disposed to form a closed magnetic circuit. Consequently, positioning error may occur, resulting in decreasing the effective facing area of these two cores and/or variation of the face-to-face gap therebetween.
The coil unit of the prior art is such that an exposed core portion extending from the primary coil bobbin is covered with a cover made of relatively flexible material, e.g., polypropylene to prevent heat cracking of resin injected and cured around the extending core portion by absorbing heat stress possibly produced in the core portion. However, the core cover material has poor adhesion to the potting epoxy resin, resulting in producing a small gap between them.
Drawbacks of the conventional ignition coil device are as follows:
Accurate face-to-face mounting of a center core and a connecting core is hardly achieved. Mismatching of end faces of these cores (with reduced effective facing area) and variation of a gap therebetween may cause degrading of magnetic characteristic of the cores forming a closed magnetic circuit.
Displacement of opposing end faces of a center core and a connecting core in a coil unit may occur, making it difficult to mount a coil unit in a coil case.
A gap may be produced between a core cover and potting resin therearound, wherefrom cracking in the cured resin may initiate.